1. Field of the Invention
The present invention relates generally to a magnetic tape cassette, particularly to a magnetic tape cassette comprising a pair of tape reels each having a pair of reel flanges, a magnetic tape cassette casing formed of upper and lower halfs, and a pair of reel lock arms provided within the casing so as to restrict rotation of the pair of reels, when the tape cassette is out of a recording and/or reproducing apparatus.
2. Description of the Prior Art
Magnetic tape cassettes comprising two magnetic tape reels and a magnetic casing are common.
Recently, there have been proposed and developed magnetic tape cassettes provided with an opening for receiving an optical tape end detector, which detects the beginning of the tape and the end of tape and which is provided in a recording and/or reproducing apparatus, and a tape reel locking mechanism which restricts rotation of a pair of tape reels when the cassette is not in the apparatus and is released so as to allow the smooth rotation of the tape reels when the cassette is in use. Such a prior art VTR tape cassette is shown in FIGS. 1 and 2.
As shown in FIG. 1, the lower half of the casing 1 is provided with an opening 2 for receiving a lock releasing pin which is capable of releasing the engagement between a pair of tape reels 6 and a pair of reel lock arms 5 and which is provided in the recording and/or reproducing apparatus. The lower half of the casing is also provided with a detector opening 3 through which a light source portion of a tape end detector of the apparatus is inserted into the tape cassette. As best shown in FIG. 1, the pair of reel lock arms 5 each comprises an engaging portion 7 for engaging with grooves 12 which are formed between teeth on an outer periphery of a flange of a tape reel 6, a substantially L-shaped portion having a circular cross-section pin 8, and a cylindrical portion 9 pivotably supported by a pin 10 provided on the lower half of the casing. The engaging portion 7 is normally biased by the spring force of a spring 11 into engagement with the grooves 12. The pair of reel lock arms 5 are rotated by a lock releasing member 4 having a pushing portion 4a for pushing the pin 8, a lid portion 4b for covering the opening 2, and a shaft 4c rotatably supported by a cylindrical supporting member 16 horizontally provided on the lower housing 1, when the lock releasing pin is inserted into the opening 2. The releasing operation of the reel lock arms 5 will be hereinbelow described.
As seen clearly in FIG. 2, the lock releasing member 4 is urged by the lock releasing pin 17 to rotate about its shaft 4c and as a result the pushing portion 4a pushes the pair of pins 8, thereby rotating the reel lock arms out of engagement with the grooves 12 and thus the pair of reels become free to rotate.
As set forth above, such VTR tape cassettes require two openings, namely, the first opening 2 for receiving the lock releasing pin 17 and a second opening 3 for receiving the optical tape end detector. The first opening 2 is covered by a lid portion 4b, but the second opening 3 remains open and as a result dust tends to get into the cassette casing. Furthermore, it may be conceived that the tape end detector could double as the lock releasing pin. However, the distance that the light source portion projects into the cassette casing is larger than the corresponding projection distance of the lock releasing pin, even though the lock releasing member 4 is rotated, the large amount of rotation of the lock releasing member 4 necessary to permit operation as the tape end detector is impossible because the internal space of the cassette casing is limited.
A magnetic tape cassette with a reel lock mechanism, in which a single opening receives a tape end detector which also functions to release the reel locking mechanism, has been disclosed in the Japanese Patent First Publication (Jikkai Showa) 58-109873. In such a magnetic tape cassette, a reel lock arm is moved by a cam surface which is formed on the top end of the tape end detector and which is conical. However, in this construction, the amount of movement of the reel lock arm is proportional to the diameter of the top end. Therefore, when the desired amount of the movement is required, a relatively large diameter conical cam portion is required. As a result, the size of the reel lock mechanism is increased. Furthermore, with this construction the problem remains that there is a hole in the casing through which dust can enter.